Liners of this general type are already known. One such is described in U.S. Pat. No. 4,751,799. It comprises a plurality of superposed sections. The liner is formed with integral T-shaped sections extending externally thereof and enabling the liner to be keyed to a surrounding mass of cast material. The liner prevents toxic materials from reaching the cast material. This arrangement is unnecessarily complex and adds to on site work.
According to the present invention there is provided a liner for a manhole, inspection chamber or the like comprising one or more sections moulded from a synthetic plastics material, the one or more each section comprising inner and outer skins joined by a system of webs to provide a substantially rigid deformation resistant structure and the opposite ends of which are formed to interlock with any adjacent section.
In a preferred embodiment of the invention, there are two series of webs. The webs of both series extend at right angles to and between the inner and outer skins. Those of a first series are located adjacent one end of the section and those of the second series extend between a position displaced from that surface and the surface at he opposite end of the section. One end of the section is rebated to form a projection which extends all the way around the periphery of the section and the other end of the section is formed in complementary manner. In this way superposed sections can be interlocked, the projection of one section interlocking with the complementary formation of the section directly adjacent it. In an installation of the liner, the lowermost section would sit on a prepared base usually of concrete and a lid would be placed over the uppermost section. The undersurface of the lid would advantageously be provided with a complementary formation to that of the upper surface of the uppermost section.